This invention relates to an axial fan for a radiator of a motor vehicle engine whose fan hub is fastened by means of a fan flange while leaving an annular gap on a clutch housing of a fluid friction clutch which can be driven by a driving part of the motor vehicle engine.
Axial fans are known which rotate at low speeds of motor vehicles for ventilating the radiator of a coolant circulating system of the motor vehicle. By means of a fluid friction clutch, such axial fans are driven directly by the motor vehicle engine. For the transmission of force, either a V-belt is used, or the driving part of the fluid friction clutch is mounted directly on the crankshaft of the motor vehicle engine. The fluid friction clutch has a clutch housing whose outer edge is provided with radially projecting cooling fins. A fan hub of the axial fan encloses the clutch housing radially on the outside and is rigidly fastened on the clutch housing. In order to permit a flow around the cooling fins of the clutch housing, an annular gap is provided between the fan hub and the clutch housing. As a result of the annular gap between the fan hub and the clutch housing, however, return flows and swirls frequently occur in the operation of the axial fan which have a negative influence on the flow conditions of the axial fan and thus reduce the efficiency of the axial fan.
It is an object of the invention to provide an axial fan of the initially mentioned type which is improved fluidically.
This object is achieved according to preferred embodiments of the invention in that, on the fan hub, an air guiding ring is provided on an inlet side relating to the flow direction of the air flow, which air guiding ring has a curved profile which is directed axially opposite to the flow direction and is curved radially toward the inside. As a result, an improved distribution of the air guiding is achieved. On the one hand, the air guiding of the main flow takes place by the providing of an air guiding ring radially on the outside along the fan hub and past the blades of the axial fan. On the other hand, by means of the air guiding ring, the air guiding of an auxiliary flow takes place for cooling the cooling fins of the clutch housing in a targeted manner between the clutch housing and the fan hub without any generating of return flows or swirls. As a result, swirl areas in the hub range of the axial fan are reduced whereby a pressure equilibrium can be created. In addition, an increase of the efficiency of the axial fan is achieved.
As a further development of the invention, a forward facing front edge of the air guiding ring is arranged at an axial distance to an outer edge of the clutch housing, and this front edge projects beyond the outer edge radially to the inside. As a result, the "spoiler effect" of the air guiding ring is further improved.
In a further development of the invention, the air guiding ring is a component which is separate from the fan hub and which is detachably fastened on the fan hub. As a result, it is possible to attach the air guiding ring as an additional part to existing axial fans without any high expenditures. The detachable fastening of the air guiding ring nevertheless ensures a simple removal of the fluid friction clutch from the fan hub.
In a further development of the invention, the air guiding ring has several fastening projections which are distributed along its circumference and which adjoin the fan hub radially from the inside and project axially between the reinforcing fins of the fan hub. Particularly fastening brackets are suitable as the fastening projections. By means of this further development, it is possible to connect the air guiding ring by means of a simple fastening of the fastening brackets on the fan hub rigidly with this fan hub. Advantageously, an undetachable detent connection is provided for this purpose.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.